Specifications

A relatively modern design of locomotive (loosely developed from the earlier Class D49 4-4-0 type) it has piston valves and three cylinders. The inside cylinder is driven by the Gresley Conjugated Valve Gear (a development of the Walschaert valve gear) by which the valve for the centre cylinder has its motion derived from the two outer cylinders. The outside cylinders drive the centre axle and the inside cylinder drives the front axle. It features a round topped boiler, with the characteristic gracefully curved Gresley running plate, with the nameplate positioned on the splasher over the centre driving wheels.

Because of its Great Eastern heritage some of the locomotives were fitted with air brakes in addition to the more customary vacuum brakes. For those so fitted the air pump was on the right hand side of the locomotive adjacent to the smoke box, with the air brake hose on the buffer beam next to the vacuum hose. Indeed, there were three varieties of braking system, ostensibly as follows although variations occurred as time progressed:

Loco Brake

Train Brake

Locomotives

Air

Air or Vacuum

61600 - 61615

Steam

Vacuum

61616 - 61642

Vacuum

Vacuum

61643 - 61673

As is often the case there were more than one variation of the class, such being designated as B17/1, B17/4, B17/5 or B17/6. Note that the B17/5 variation was purely cosmetic with a streamlined appearance.

The original design (B17/1) required a relatively light axle loading (for the lines in East Anglia, where the class were destined to be employed) while at the same time having the necessary power to haul the increasingly heavy trains being introduced at the time. Small GE style tenders were initially required due to the short turntables then extant on the former GE section (1928). Due to initial teething problems numerous design changes were implemented to improve the draughting, the springing and, in particular, the frames which in their original form were prone to cracking.

Later designs includied these improvements and also saw the introduction of the larger LNER style tenders. These locos were designated B17/4s and were intended for use on longer journeys on the former GC section where the civil engineering restrictions of East Anglia did not apply. As the track in former GE section was improved and bridges strengthened (along with the introduction of larger turntables) the low weight and short wheelbase of the original class members became less a factor and allowed the use of the LNER style tenders throughout the system.

The final improvement was the introduction of the 100A diagram boiler defining the B17/6s. Some of the class were fully rebuilt by Thompson as a two cylinder locomotive to form the B2 class, which was essentially a B1 with large driving wheels.